This invention relates to apparatus and a method for detecting of the completion or end point of a cleaning process for a chamber used in semiconductor processing.
In the manufacturing of semiconductor devices, such as integrated circuits, memories, etc., a semiconductor wafer (e.g., a thin disc of single-crystal silicon) is sequentially put through a number of processing steps. Typically one or more of these steps involves exposing the wafer to a mixture of reactive gasses to deposit thin layers of insulation, such as silicon dioxide (SiO2), on exposed surfaces of the wafer. The reactive gasses comprise, for example, ozone or oxygen on the one hand and an organic vapor of a liquid, such as tetraethylorthosilicate (TEOS), in an inert gas such as helium on the other hand.
During such deposition of an insulation layer, a wafer typically sits on a chuck in a sealed processing chamber while a thin film of solid material (e.g., SiO2) is formed on an exposed surface of the wafer. However, the gaseous compound within the chamber from which the thin film is being formed on the wafer likewise, though undesirably, deposits solid material (e.g., SiO2) on inside walls of the chamber and on other exposed surfaces within it. Such undesirable deposits, if allowed to accumulate, produce dust and particles which can contaminate subsequent wafers when they afterward are processed in the chamber. It is necessary therefore to periodically clean the chamber of such deposits.
In the past various ways of cleaning processing chambers have been employed in the semiconductor industry. One way of cleaning, termed wet-cleaning, is to open a chamber and to manually wipe down its inside wall and surfaces. This involves a considerable loss of production time of the equipment, and requires expensive hand labor. Another way of cleaning a chamber, termed dry cleaning, is to employ a plasma-excited cleaning gas, such as fluorine, NF3, CxFy, or SF6, to chemically etch away the unwanted solid deposits inside the chamber. With previous systems it has been difficult to tell when the dry cleaning operation has been completed. As a result, the cleaning process is often continued considerably beyond the point at which the chamber is clean. Thus, additional time is used which limits throughput and increases the danger of unwanted etching of the chamber walls by unnecessarily prolonging the cleaning process to be sure that solid deposits have been all cleaned away. It is desirable to have a more efficient and cost-effective way of detecting an end point of cleaning.
In one aspect, the present invention includes apparatus which comprises a semiconductor processing chamber, an optical temperature sensor located within the chamber, and a controller. The semiconductor processing chamber has electrical elements which help facilitate a plasma in the chamber from cleaning gases introduced into the chamber. The controller has an input coupled to an output of the optical temperature sensor and is adapted to control a flow of cleaning gases into the chamber such that during a cleaning operation of the chamber the flow of cleaning gases is cutoff when the plasma temperature reaches a value indicative of completion of cleaning.
In another aspect, the present invention includes apparatus for processing semiconductor wafers. The apparatus comprises a processing chamber, a support member within the chamber having a surface capable of supporting a wafer during processing, a fiberoptic cable having a first end positioned near the surface of the support member, an optical pyrometer, and a computer. The optical pyrometer is connected to a second end of the cable and measures the temperature of a wafer during processing and for thereafter measures in situ temperature of plasma-excited cleaning gas in the chamber during subsequent cleaning away of unwanted solid deposits within the chamber. The computer is coupled to the pyrometer for determining how soon after cleaning is started the temperature of the plasma-excited gas reaches a value indicative of a cleaning end point and for thereupon stopping the cleaning operation.
In a further aspect, the present invention includes apparatus for chemical vapor deposition (CVD) of materials onto semiconductor wafers. The apparatus comprises a processing chamber, a chuck within the chamber and having a surface for supporting a wafer during CVD processing, a fiberoptic cable having a first end positioned at the surface of the chuck, an optical pyrometer, a gas supply, electrodes, a gas outlet, and a computer. The optical pyrometer is connected to a second end of the cable for measuring temperature of a wafer during processing and for thereafter measuring in situ temperature of plasma-excited cleaning gas in the chamber during subsequent cleaning away of unwanted solid deposits within the chamber. The gas supply admits cleaning gas into the chamber. The electrodes generate a plasma-discharge in the cleaning gas. The gas outlet exhausts cleaning and other gases downward from the chuck and out of within the chamber. The computer is coupled to the pyrometer for determining how soon after cleaning is started the temperature of the plasma-excited gas reaches a value indicative of an end point of cleaning. The computer controls the gas supply, the electrodes, and the gas outlet to stop the cleaning operation when the end point value temperature is detected.
From a first method aspect, the present invention includes a method of cleaning a semiconductor chamber of undesirable deposits. The method comprises the steps of: flowing cleaning gases into the chamber; generating a plasma from the cleaning gases; optically measuring the temperature within the chamber as the cleaning gases flow into the chamber; and terminating the flow of cleaning gases into the chamber when the temperature within the chamber reaches a value indicative of completion of cleaning.
In an additional aspects the present invention includes a method for cleaning a semiconductor processing chamber of solid material deposited thereon during chemical vapor deposition (CVD) of a layer of material on to a wafer processed in the chamber. The method comprising the steps of: flowing cleaning gas into the chamber; establishing a plasma-discharge in the cleaning gas; measuring via a fiberoptic cable and an optical pyrometer the in situ temperature of the plasma-excited cleaning gas as it removes deposits of solid material left in the chamber from previous CVD processing of a wafer; monitoring the change in temperature versus time of the plasma-excited cleaning gas to determine when the temperature reaches a value indicative of a cleaning end point; and terminating the cleaning process when the temperature reaches the cleaning end point value.
From an additional aspect, the present invention includes method of chemical vapor deposition (CVD) of solid material onto a semiconductor wafer and for then cleaning the chamber of unwanted solid residues left in the chamber after such processing. The method comprises the steps of: depositing solid material on a wafer by CVD processing in the chamber; measuring temperature from one side of the wafer during processing the temperature thereof using a fiberoptic cable and optical pyrometer; removing the wafer from the chamber; admitting cleaning gas into the chamber to remove unwanted deposits of solid material left after the CVD processing; plasma-exciting the cleaning gas; using the fiberoptic cable and pyrometer to measure in situ the temperature of the cleaning gas as it cleans away unwanted solid deposits; monitoring the temperature versus time of the plasma-excited cleaning gas to determine an end point of cleaning as indicated by temperature of the plasma-excited gas rising from an initial value to a steady-state value; evacuating cleaning gas mixed with gassified portions of the solid material to maintain a desired pressure in the chamber; and terminating the cleaning process when the steady-state temperature is reached.
A better understanding of the invention will best be gained from the following description given in conjunction with the accompanying drawings and claims.